Accurate estimation of the state-of-charge (SOC) of batteries is critical for both electric vehicle (EV) and hybrid electric vehicle (HEV) applications. For EV applications, the SOC determines the travel range for the passenger. For HEV applications, the power limits of the battery are often a function of SOC, thus accurate SOC estimation is essential to safe and efficient battery pack operation. Existing techniques for determining SOC often use the battery open-circuit voltage (OCV) to estimate SOC, using a table of pre-determined values that relate OCV to SOC. Other factors, such as battery temperature and battery age may also be included in the determination of SOC.